JP2004156775A - Screw fastening structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide screw fastening structure to sheet metal improving repeated fastening performance while satisfying screwing torque, loosening torque and internal thread breaking torque which are basic characteristics required in screw fastening. <P>SOLUTION: A tapping screw 1 for a sheet with a lead part 6 composed of a single-start thread and with an effective thread part 7 composed of a double-start thread, is used. A recessed part 14 is formed around an internal thread prepared hole 12 of a fastening material 11 by narrowing trapezoidal sectional shape large on the beginning side of screwing with respect to the screwing direction 13 of the tapping screw 1. The diameter 15 of the base part of the recessed part 14 is larger by 0.5-0.2 mm than the maximum outer diameter of the thread part of the fastened tapping screw 1, the angle of an inclined face part is about 45°±15°, and the narrowed depth 17 is 1/4-1/2 of the plate thickness of the fastening material 11. The recessed part 4 of the fastening material 3 for screwing the tapping screw 1 is minutely deformed due to axial tension by the tapping screw 1 in the fastened state, and put in a pressurized state. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a screw fastening structure, and more particularly, to a structure suitable for fastening a tapping screw to a thin metal plate.
[0002]
[Prior art]
FIG. 8 is a cross-sectional view showing the shape of a pilot hole (burring hole) formed by a conventional projection process. In the case of the conventional fastening member 24 having a thickness of 1.2 mm to 0.8 mm, the material is squeezed by a protrusion process to secure a protrusion height 25. When a normal JIS tapping screw three-type forming type is used for such a fastening member 24, when the plate thickness of the fastening member 24 is small, the protruding portion tip 26 spreads as shown by a dotted line 27 at the time of thread rolling. However, a phenomenon that the effective screw length cannot be secured and the internal thread breaking torque decreases may occur. In addition, the fastening performance is greatly affected by variations in the dripping portion 28 of the threaded portion in the protruding process. In addition, a large press pressure is required for the burring process.
[0003]
However, conventionally, it is said that even if burring is performed on the fastening member 24 side with the JIS tapping type 3 screw, the screw cannot be fastened particularly with a thin sheet metal having a thickness of 0.6 mm or the like. In other words, the internal thread breaking torque is small on the internal thread side, making it impractical. Conventionally, when three types of screws are repeatedly fastened to a burring-shaped female screw having a thickness of 0.8 mm, the number of times of repeated fastening is less than ten times, and the female thread is broken.
[0004]
With the class 1 screw, there is a method of fastening the thin plate without burring. However, the axial force, that is, the force for pressing the material to be fastened to the fastening material is small, and repeated fastening is impossible. In other words, OA equipment cannot be used in places where securing of axial force (contact pressure), prevention of loosening, etc. are required in terms of safety standards applied to all screw tightening places.
[0005]
On the other hand, equipment is increasingly reused due to environmental considerations. In such a case, it is required that the screw can be re-fastened a plurality of times. In addition, energy saving effect by weight reduction is expected.
[0006]
Therefore, as a screw which can be repeatedly fastened to a thin plate without burring, a tapping screw for a forming-type metal thin plate having a lead portion having one thread and an effective screw portion having two threads has been considered.
[0007]
[Problems to be solved by the invention]
However, tapping screws of the above type have the disadvantage of low axial force. If the tightening torque (driver torque) is increased to improve the axial force, the material to be fastened, especially the plate thickness is 0.6 mm When a screw hole is large with a thin sheet material, female thread breakage may occur.
[0008]
An object of the present invention is to provide a screw fastening structure that can be used without burring on various plate materials without being limited to a thin plate material or the like, can be repeatedly fastened, and can secure the axial force of a screw.
[0009]
Another object of the present invention is to provide a screw fastening structure that satisfies the basic characteristics required for screw fastening, such as screwing torque, loosening torque, and internal thread breaking torque, and can improve the fastening performance repeatedly.
[0010]
[Means for Solving the Problems]
The screw fastening structure for a metal thin plate according to claim 1 of the present invention is a structure for fastening a tapping screw to a metal thin plate in order to achieve the above object, and a female screw side pilot hole into which the tapping screw is screwed. It is characterized in that a concave portion is provided around the periphery to be recessed in the screwing direction.
[0011]
According to a second aspect of the present invention, in order to achieve the above object, in the screw fastening structure to a thin metal plate according to the first aspect, the bottom diameter of the concave portion is larger than the outer diameter of the tapping screw. I do.
[0012]
According to the third aspect of the present invention, in order to achieve the above object, in the screw fastening structure for a metal thin plate according to the first or second aspect, the depth of the concave portion is set to a value corresponding to the thickness of the peripheral portion of the female screw side pilot hole. It is characterized by 1/4 to 1/2.
[0013]
According to a fourth aspect of the present invention, in order to achieve the above object, in the screw fastening structure for a metal thin plate according to any one of the first to third aspects, the concave portion has a trapezoidal cross-sectional shape in which a side from which the tapping screw is screwed is wide. It is characterized by doing.
[0014]
According to a fifth aspect of the present invention, in order to achieve the above object, in the screw fastening structure for a metal sheet according to any one of the first to third aspects, the concave portion is formed in a half-blanked shape.
[0015]
According to a sixth aspect of the present invention, in order to achieve the above object, in the screw fastening structure according to any one of the first to fifth aspects, the tapping screw has a lead portion having one thread and an effective thread portion having a thread portion. It is characterized in that it is for a forming type metal sheet having two lines.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a side view showing an example of a thin plate tapping screw 1 (hereinafter simply referred to as a tapping screw 1) used in an embodiment of the present invention. The head 5 has a hexagonal shape with a cross-recessed seat, and the threaded portion of the lead portion 6 is formed of a single thread and the effective threaded portion 7 is formed of a double thread. In the double thread of the effective thread portion 7, the threads 9, 10 are symmetrical with respect to the thread center axis 8. Therefore, even if the screw is initially tightened diagonally to the material to be fastened, the resistance on one side increases when the effective screw portion 7 is hooked on the material to be fastened, so that the effective screw portion 7 is oriented at right angles to the portion to be fastened. Is corrected. In addition, since the lead portion 6 is a single-threaded screw, it is considered that the screw is easily formed and traced easily at the time of re-fastening, and that it is very effective for repeated fastening.
[0017]
FIG. 2 is a cross-sectional view of one embodiment of the present invention in a state where the screw is fastened using the screw shown in FIG. In this embodiment, the workpiece 2 is fastened to the fastener 3 with the tapping screw 1 shown in FIG. In the fastened state, the concave portion 4 of the fastening member 3 is slightly deformed due to the axial force of the tapping screw 1 and is in a state where a preload is applied.
[0018]
FIG. 3 is a cross-sectional view of a recess around a pilot hole in the fastening member 11 having a plate thickness of 0.6 mm and 0.8 mm. Around the female screw pilot hole 12 of the fastening member 11, a concave portion 14 is formed by drawing in a trapezoidal cross-sectional shape having a wide screwing source side in the screwing direction 13 of the tapping screw 1. The diameter 15 of the bottom of the concave portion 14 is 0.5 to 0.2 mm larger than the maximum outer diameter of the thread portion of the tapping screw 1 to be fastened, and the angle 16 of the inclined surface portion is about 45 ° ± 15 °, and the aperture is further reduced. The depth 17 is set to １ ／ to の of the plate thickness of the fastening member 11.
[0019]
FIG. 4 is a cross-sectional view of a recess around a prepared hole in the fastening member 18 having a thickness of 1.0 mm. Around the internal thread 19 of the fastening member 18, there is formed a concave portion 21 formed by half-cutting in the screwing direction 20 of the tapping screw 1. The diameter 22 of the concave portion 21 is 0.5 to 0.2 mm larger than the maximum outer diameter of the tapping screw 1 to be fastened, as in the example in FIG. It is 1/4 to 1/2.
[0020]
In both examples of FIGS. 3 and 4, the diameters and depths of the bases and the like of the concave portions 14 and 21 are set from the viewpoint that the bending strength due to the shape effect around the prepared hole can be secured and the processing can be easily performed. . Further, the difference between the drawing process and the half blanking process was also selected from the viewpoints of ease of processing and securing of strength due to the thickness of the fastening members 11 and 18. Note that the drawing pressure and the half blanking processing require less press pressure than burring.
[0021]
FIG. 5 is a cross-sectional view of an example in which a flat thin fastening member 29 having no concave portion is fastened as a comparative example. Around the female screw hole 30 of the fastening member 29, a bending moment about the screw hole end 33 of the workpiece 32 acts as a fulcrum due to the axial force of the screw 31, and deformation occurs. The deformation due to the bending stress is a major factor in the internal thread breaking. On the other hand, in both of the examples of FIGS. 3 and 4, the periphery of the internal thread pilot holes 12 and 19 has a shape resistant to bending stress, and the internal thread fracture is well prevented.
[0022]
[Experimental example]
FIG. 6 is a diagram of the internal thread breaking torque effect due to the presence or absence of the concave portion as in the embodiment of the present invention described above. FIG. 6 shows the result of measuring the internal thread breaking torque when a screw having a nominal diameter of 3 (not shown) is used. Show. Numeral 34 in the figure indicates the fracture torque characteristic of the female thread having a concave portion of the fastening material having a thickness of 0.6 mm. The internal thread breaking torque of a fastening material with a plate thickness of 0.6 mm and no recesses is 1.1 N · m or less because female threads are broken when tightened with a tightening torque of 11 kgf · cm (1.078 N · m). it is conceivable that. As the effect of the presence of the concave portion, the performance is improved by about 87 to 62% in the pilot hole diameter measured this time.
[0023]
Also, in the figure, 35 shows the female thread breaking torque characteristic of a 0.8 mm thick fastening material with a concave portion, and 36 in the figure shows the female thread breaking torque characteristic of a 0.8 mm thick fastening material without a concave portion. . The performance of each pilot hole diameter is improved by about 50%.
[0024]
Note that the internal thread fracture is caused by insufficient bending stress due to an increase in the distance between the internal thread end portion and the holding portion on the side to be fastened. With a hole of 3.5 mm × 5 mm and a tightening torque of 1.1 N · m, the internal thread was frequently destroyed without the concave portion, and the internal thread was not destroyed with the concave portion.
[0025]
FIG. 7 is a diagram of the loosening torque effect due to the presence or absence of the concave portion as in the above-described embodiment of the present invention, and shows the result of the loosening torque measurement when a screw (not shown) having a nominal diameter of 3 is used. In the drawing, reference numeral 37 denotes the loosening torque characteristic with a plate thickness of 0.6 mm and a concave portion. With the same plate thickness, without the concave portion, measurement was impossible due to the occurrence of internal thread breakage (loose torque = 0). In the drawing, reference numeral 38 denotes a loose torque characteristic with a recess having a thickness of 0.8 mm, and reference numeral 39 denotes a loose torque characteristic without a recess having the same thickness.
[0026]
As can be seen from the results, the performance of the pilot hole diameter measured this time is approximately 30% improved. This is thought to be due to the fact that the distortion in the concave portions 14 and 21 functions as loosening prevention in the same manner as when a dishwasher is inserted.
[0027]
When the internal thread plate thickness was 0.8 mm, the average breaking torque of the internal thread was 1.42 N · m without the concave portion and the average breaking torque of the internal thread was 2.14 N · m without the concave portion, and the loosening torque was improved by about 30%. Further, when the plate thickness was 0.8 mm, the average loose torque when there was no concave portion was 0.58 N · m, and the average loose torque when there was a concave portion was 0.77 N · m.
[0028]
That is, in places where axial force is required in the past, a steel plate with a thickness of 0.6 mm, which could not be used because screws could not be tightened, can be used, and a plate material with a thickness of 0.8 mm is converted to a thinner plate material Can be achieved, resulting in significant cost reduction and, consequently, energy saving. In addition, even when the thickness of the used material is 0.6 mm, compared with the conventional thickness of 0.8 mm and the fastening performance by burring, the improvement of the internal thread breaking torque, the repetitive fastening performance is greatly improved, and the reusability is improved. .
[0029]
Furthermore, even when switching from conventional burring processed parts with a sheet thickness of 0.8 mm, the burring processing is changed to half-pressing processing, the processing press pressure is reduced, the workability is improved, and the repetitive fastening performance is greatly improved. To improve. Even if the thickness of the material used is 1.0 mm, it can be fastened by simple drilling instead of the conventional burring, or if a larger internal thread breaking torque is required, half punching is used. The performance is improved.
[0030]
That is, when the thickness to be fastened is small, the bite of the incompletely threaded male thread into the female thread is reduced, and the fastener can be fastened without providing the female thread with a burring process. It is possible to make use of the characteristics of a tapping screw for a forming-type metal thin plate having an effective screw portion having two threads. Of course, other types of self-tapping screws can also achieve the same effect.
[0031]
【The invention's effect】
As described above, the screw fastening structure according to the present invention secures the axial force of the screw and enables fastening without providing burring processing on the female thread portion, and has an effect of improving loosening prevention performance. .
[Brief description of the drawings]
FIG. 1 is a side view showing an example of a thin plate tapping screw used in an embodiment of the present invention.
FIG. 2 is a cross-sectional view of one embodiment of the present invention.
FIG. 3 is a cross-sectional view of a recess around a pilot hole of a fastening material having a plate thickness of 0.6 mm and 0.8 mm according to an embodiment of the present invention.
FIG. 4 is a cross-sectional view of a recess around a pilot hole made of a fastening material having a thickness of 1.0 mm according to an embodiment of the present invention.
FIG. 5 is a cross-sectional view of a comparative example in which a flat thin plate fastening material having no recess is fastened.
FIG. 6 is a diagram of the internal thread breaking torque effect depending on the presence or absence of a concave portion as in the embodiment of the present invention.
FIG. 7 is a diagram illustrating a loosening torque effect depending on the presence or absence of a concave portion as in the embodiment of the present invention.
FIG. 8 is a cross-sectional view showing a pilot hole shape formed by a conventional protrusion process.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Tapping screw for thin plates 2 Material to be fastened 3 Fastening material 4 Recess 5 Head 6 Lead part (single thread)
7 Effective thread (double thread)
8 Screw center axis 9, 10 Screw thread 11, 18 Fastening material 12, 19 Female screw pilot hole 13, 20 Screwing direction of tapping screw 14 Trapezoidal cross section concave part 21 Concave part with half blanking

Claims (6)

A screw for fastening a tapping screw to a thin metal plate, wherein a recessed portion that is recessed in the screwing direction is provided around a female screw side pilot hole into which the tapping screw is screwed. Fastening structure. 2. The screw fastening structure according to claim 1, wherein a bottom diameter of the concave portion is larger than an outer diameter of the tapping screw. 3. The screw fastening structure according to claim 1, wherein the depth of the concave portion is set to 1/4 to 1/2 of the thickness of the female screw side pilot hole. The screw fastening structure according to any one of claims 1 to 3, wherein the recess has a trapezoidal cross-sectional shape on a side where the tapping screw is screwed. The screw fastening structure according to any one of claims 1 to 3, wherein the recess has a half-blanked shape. 6. The screw fastening structure according to claim 1, wherein said tapping screw is for a forming-type metal sheet having a lead portion having one thread and an effective screw portion having two threads. A screw fastening structure characterized by the following.

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